Studies on Horseradish Peroxidase. XIII. The Kinetic Effect of Cyanide on the Oxidation–Reduction Cycle

1973 ◽  
Vol 51 (5) ◽  
pp. 627-631 ◽  
Author(s):  
M. L. Cotton ◽  
H. B. Dunford ◽  
J. M. T. Raycheba
Keyword(s):  
Steady State ◽  
Horseradish Peroxidase ◽  
Kinetic Effect ◽  
Ph Values ◽  
Oxidation Reduction ◽  
Reduction Cycle ◽  
Native Horseradish Peroxidase ◽  
Soret Region

The effect of cyanide on the steady-state oxidation of ferrocyanide by horseradish peroxidase was studied at pH values 9.00, 7.10, and 5.00. An inhibition was observed which could be explained by the binding of cyanide only to native horseradish peroxidase. Spectra in the Soret region supported these conclusions.

scholarly journals Phorbol esters and horseradish peroxidase stimulate pinocytosis and redirect the flow of pinocytosed fluid in macrophages.

1985 ◽  
Vol 100 (3) ◽  
pp. 851-859 ◽  
Author(s):  
J A Swanson ◽  
B D Yirinec ◽  
S C Silverstein
Keyword(s):  
Steady State ◽  
Horseradish Peroxidase ◽  
Phorbol Esters ◽  
Lucifer Yellow ◽  
Fluid Phase ◽  
Peritoneal Macrophages ◽  
Tumor Promoter ◽  
Steady State Rate ◽  
Reduced Rate ◽  
Rate Of Accumulation

Lucifer Yellow CH (LY) is an excellent probe for fluid-phase pinocytosis. It accumulates within the macrophage vacuolar system, is not degraded, and is not toxic at concentrations of 6.0 mg/ml. Its uptake is inhibited at 0 degree C. Thioglycollate-elicited mouse peritoneal macrophages were found to exhibit curvilinear uptake kinetics of LY. Upon addition of LY to the medium, there was a brief period of very rapid cellular accumulation of the dye (1,400 ng of LY/mg protein per h at 1 mg/ml LY). This rate of accumulation most closely approximates the rate of fluid influx by pinocytosis. Within 60 min, the rate of LY accumulation slowed to a steady-state rate of 250 ng/mg protein per h which then continued for up to 18 h. Pulse-chase experiments revealed that the reduced rate of accumulation under steady-state conditions was due to efflux of LY. Only 20% of LY taken into the cells was retained; the remainder was released back into the medium. Efflux has two components, rapid and slow; each can be characterized kinetically as a first-order reaction. The kinetics are similar to those described by Besterman et al. (Besterman, J. M., J. A. Airhart, R. C. Woodworth, and R. B. Low, 1981, J. Cell Biol. 91:716-727) who interpret fluid-phase pinocytosis as involving at least two compartments, one small, rapidly turning over compartment and another apparently larger one which fills and empties slowly. To search for processes that control intracellular fluid traffic, we studied pinocytosis after treatment of macrophages with horseradish peroxidase (HRP) or with the tumor promoter phorbol myristate acetate (PMA). HRP, often used as a marker for fluid-phase pinocytosis, was observed to stimulate the rate of LY accumulation in macrophages. PMA caused an immediate four- to sevenfold increase in the rate of LY accumulation. Both HRP and PMA increased LY accumulation by stimulating influx and reducing the percentage of internalized fluid that is rapidly recycled. A greater proportion of endocytosed fluid passes into the slowly emptying compartment (presumed lysosomes). These experiments demonstrate that because of the considerable efflux by cells, measurement of marker accumulation inaccurately estimates the rate of fluid pinocytosis. Moreover, pinocytic flow of water and solutes through cytoplasm is subject to regulation at points beyond the formation of pinosomes.

Fundamental and Technological Aspects of Actinide Oxide Pyrochlores: Relevance For Immobilization Matrices

1999 ◽  
Vol 556 ◽  
Author(s):  
P. E. Raison ◽  
R. G. Haire ◽  
T. Sato ◽  
T. Ogawa
Keyword(s):  
Elevated Temperatures ◽  
Materials Science ◽  
Oxidation Potential ◽  
Oxygen Stoichiometry ◽  
X Ray Diffraction ◽  
X Ray ◽  
Oxidation Reduction ◽  
Reduction Cycle ◽  
Fluorite Type ◽  
The Stability

AbstractPolycrystalline pyrochlore oxides consisting of selected f elements (lanthanides and actinides) and Zr and Hf have been prepared and characterized. Characterization to date has been primarily by X-ray diffraction, both at room and at elevated temperatures. Initial studies concentrated on selected lanthanides and the Np, Pu and Am analogs (reported here) but have been extended to the other actinide elements through Cf. Data from these studies have been used to establish a systematic correlation regarding the fundamental materials science of these particular pyrochlores and structurally related fluorite-type dioxides. In addition to pursuing their materials science, we have addressed some potential technological applications for these materials. Some of the latter concern: (1) immobilization matrices; (2) materials for transmutation concepts; and (3) special nuclear fuel forms that can minimize the generation of nuclear wastes. For f elements that display both a III and IV oxidation state in oxide matrices, the synthetic path required for producing the desired pyrochlore oxide is dictated by their pseudo-oxidation potential the stability of the compound towards oxygen uptake. For the f elements that display an oxidationreduction cycle for pyrochlore-dioxide solid solution, X-ray diffraction can be used to identify the composition in the oxidation-reduction cycle, the oxygen stoichiometry and/or the composition. This paper concentrates on the Np, Pu and Am systems, and addresses the above aspects, the role of the crystal matrix in controlling the ceramic products as well as discussingsome custom-tailored materials.

The Electrochemical Evaluation of the Metal-Carbon Bond Energies (−ΔGBF) of Alkylated Iron and Cobalt Porphyrins [(por)M-R]

1997 ◽  
Vol 01 (02) ◽  
pp. 125-134 ◽  
Author(s):  
AIMIN QIU ◽  
DONALD T. SAWYER
Keyword(s):  
Iron Porphyrins ◽  
Carbon Bond ◽  
Reduction Potentials ◽  
Oxidation Reduction ◽  
Alkyl Derivatives ◽  
Controlled Potential Electrolysis ◽  
Reduction Cycle ◽  
Cobalt Porphyrins ◽  
Controlled Potential ◽  
The Difference

The electron-transfer oxidation-reduction chemistry for the alkyl derivatives of iron and cobalt porphyrins [( por ) M III − R ] has been characterized on the basis of cyclic voltammetric and controlled-potential-electrolysis measurements. The electrogenerated anions of iron and cobalt porphyrins [( por ) M − and ( por −·) M −] are strong nucleophiles that react with alkyl halides ( RX ) via a nucleophilic displacement process to form metal-carbon bonds [( por ) M - R and ( por −·) M - R ]. The difference in the reduction potentials for RX and ( por ) M II provides an approximate measure of the ( por ) M - R bond-formation free energy (−ΔG BF ). The −ΔG BF values for iron porphyrins (14–35 kcal mol−1) and for cobalt porphyrins (20-38 kcal mol−1) depend on the electron density of the porphyrin ring ( OEP > TPP > Cl 8 TPP > F 20TPP) and the structure of the alkyl group (1° > 2° > 3°). Thus, the apparent metal-carbon bond energy (−ΔG BF ) for ( OEP ) Fe III- Bu -n is 28 ± 2 kcal mol−1, and for [( MeO )4 TPP ] Co III- Bu -n is 36 ± 2 kcal mol −1. The ( por −·) M − dianions react with carbon dioxide in an electrocatalysed reduction cycle to give CO and CO 32− via the apparent transient formation of a metal-carbon bond [( por −·) M - C ( O ) O −; −Δ G BF ≥ 12 kcal mol −1 for iron porphyrins].

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